This invention relates in general to vacuum deposition technology. More particularly, the invention relates to inhibiting the deposition of materials onto surfaces within a vacuum.
Vacuum deposition of materials is used in processes such as the formation of electrical devices (e.g., thin film resistors and capacitors), semiconductor devices (e.g., integrated circuits), optical interference film, reflective surfaces and the manufacture of devices with decorative or utilitarian metal patterns. Typically these processes are carried out by heating the source material within a vacuum chamber or bell jar so that a vapor stream of the material is created which subsequently condenses on surfaces within the chamber. Another method which has been employed to form thin films is by the cathode sputtering of a material within a vacuum chamber.
In conventional procedures of the foregoing nature, there are problems in controlling deposition of the material onto the various surfaces within the chamber. Heretofore the selective coating of surfaces by vacuum deposition has been difficult or impossible due to the susceptability of the substrate material and thin films present on the substrate to etchants or other thin film removing and masking techniques.
L. Holland describes at page 260 of his book Vacuum Deposition of Thin Films that zinc vapor will not condense on a greasy surface, such as a surface coated with a film of wax or with a silicone diffusion pump oil. The book describes the use of the coatings to provide unmetallized bands and to keep observation windows clear from zinc deposits. However, such coatings are unsatisfactory in view of the difficulty in applying the coatings and in forming patterns of the coating, the contaminating nature of the fluids for many deposition applications, the poor deposition inhibiting properties for many materials, and the inability to form extremely thin films and patterns with good linewidth resolutions.
Upon completion of vacuum deposition, it has heretofore been necessary to clean residual condensed material from the inside surfaces of the chamber. Where masks are used in the path of the vapor stream for depositing material in patterns, it has also been necessary to clean condensed material from the masks themselves. Furthermore, the inside surfaces of the viewing windows or sightglass within a vacuum chamber become obscured or fogged during vacuum deposition, making it difficult to observe the deposition processes. These viewing surfaces must also be cleaned periodically.
Conventional vacuum deposition techniques for fabricating electrical devices such as resistors and capacitors are carried out by film deposition through masks. Vacuum deposition is used to fabricate electronic devices such as semiconductors and integrated circuits by means of photolithography and etching. The photoetching techniques employ the formation of etchant-resist patterns photographically. In multiple layer work such as for integrated circuits, the formation of each layer of deposited material requires separate application of a photoresist coating followed by photoexposure of the desired pattern image, development and post-baking, chemical etching of the thin film pattern, and removal of the photoresist mask. Such techniques are relatively expensive, time consuming and have a high labor content. It would be desirable to provide a simplified method by which the various layered patterns are formed on a substrate without the requirement of using the photographic etchant-resist process.
Heretofore it has been difficult or impossible to vacuum deposit materials onto irregular or blind surfaces which are not in a line of sight with the source, such as cavities, channels, holes or the reverse side of a target object. Methods which have been employed in an attempt to overcome these problems are the use of multiple evaporation sources arrayed about the object, or the use of a planetary system to rotate the object during the evaporation process. In many cases these methods have not been satisfactory. Reasonably uniform coatings on irregular surfaces such as insects have in the past been applied using complex mechanical movements to change the angle of incidence of the vapor streams. However, it has been difficult to form uniform coatings on biological specimens which are to be examined by scanning electron microscopes. A further problem is in forming a uniform film over a semiconductor having stepped layers, such as along the edges formed in oxide layers by etching.